1. Field of the Invention
The present invention relates to a glass substrate by which light incident on a side surface can be transmitted rearward efficiently, and a transmission type or transmission-reflection type liquid-crystal display device using the glass substrate as a cell substrate and excellent in display quality.
The present application is based on Japanese Patent Application No. 2000-309989, which is incorporated herein by reference.
2. Description of the Related Art
Greater reduction in thickness, size and weight of liquid-crystal display devices has been demanded for the purpose of suppressing increase in weight which is accompanied by increase in size of television and personal computer display screens, for the purpose of reducing in size and weight of portable personal computers and portable telephone sets, etc. In the meanwhile, it is however difficult to reduce thickness, size and weight of a liquid-crystal display device if the display device is provided with a background-art front light 8 or a background-art backlight 8 including a side light pipe 83 as shown in FIGS. 5 to 7. Incidentally, the side light pipe is set to have a thickness not smaller than 1 mm for meeting the requirement of light transmission. When a light diffusing plate, a reflection plate, a prism sheet, etc. are disposed on the side light pipe, the total thickness generally reaches a vale of not smaller than 3 mm. Incidentally, the reference numeral 81 designates a light source; and 82, a light source holder.
Upon the aforementioned circumstances, there has been proposed a reflection type liquid-crystal display device in which a light source is disposed on one of side surfaces of a liquid-crystal display panel so that illumination light incident on the side surface is totally reflected in a visual side cell substrate while being transmitted in the whole panel and so that the reflected light is scattered on a roughened surface type reflection plate so as to be used for display (Unexamined Japanese Patent Publication No. Hei. 5-158033). This proposal aims at making the liquid-crystal panel also play the role of a side light pipe to omit the light pipe to thereby achieve reduction in thickness and weight of the liquid-crystal display device. Incidentally, light is transmitted in the whole liquid-crystal display panel, and particularly, the light is mainly transmitted in the cell substrate of the liquid-crystal cell.
It is however found that a background-art glass substrate satisfying performance requirements such as transparency, heat resistance, chemical resistance, surface smoothness, gas barrier characteristic, etc. has a problem that the difference between brightness and darkness is large on the panel surface because the glass substrate lacks light transmission efficiency so that display becomes darker as the position of display goes farther from the light source.
An object of the present invention is to provide a glass substrate in which light incident on a side surface can be transmitted rearward efficiently while full use of the merit of thin and lightweight characteristic can be made, and to develop a transmission type or transmission-reflection type liquid-crystal display device excellent in luminance and uniformity of luminance and good in display quality.
According to the present invention, there is provided a glass substrate constituted by a transparent glass plate, a transparent layer with a refractive index lower than that of the transparent glass plate, and an electrically conductive layer disposed on the transparent glass plate through the low-refractive-index transparent layer. There is further provided a liquid-crystal display device constituted by a liquid-crystal display panel including a liquid-crystal cell having a visual side cell substrate, aback side cell substrate, an electrode provided on the visual side cell substrate, an electrode provided on the back side cell substrate, and liquid crystal held between the visual side cell substrate and the back side cell substrate which are disposed so that the electrode sides of the two cell substrates face each other, wherein at least one of the visual side and back side cell substrates is constituted by the glass substrate.
Light incident on a side surface is confined in the glass substrate according to the present invention because of the light totally reflected by the low-refractive-index transparent layer so that the light can be efficiently transmitted (rearward) toward an opposite side surface to the incidence side surface. Moreover, the glass substrate is thin in thickness and light in weight because the weight of the glass substrate is increased only by the added weight of the low-refractive-index transparent layer. As a result, when a liquid-crystal cell is formed by use of the glass substrate as a cell substrate, incident light from a light source disposed on one of side surfaces of a liquid-crystal display panel can be transmitted rearward efficiently through the substrate. When the optical path of the transmitted light is changed to a viewing direction through suitable optical path changing means, good display quality can be achieved so that the whole display screen is bright and excellent uniformity of brightness is obtained. Moreover, a liquid-crystal display device thin in thickness can be formed when the light source is disposed on a side surface.
In the above description, if no low-refractive-index transparent layer is provided, the transmitted light in the panel enters a liquid-crystal layer or a color filter layer generally disposed adjacently to the liquid-crystal layer. As a result, the absorbed component of light into the liquid-crystal layer may increase because of birefringence of the liquid-crystal layer when the light enters a polarizer, or the rearward transmission efficiency may be lowered remarkably because of light absorption into the color filter layer. As a result, the display screen becomes darker as the position of display goes farther from the light source, so that uniformity of luminance is spoiled greatly to make it difficult to view the display.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.